The former Without a Trace producer replaced creator/executive producer Janet Tamaro as showrunner in November, just three months after star Lee Thompson Young committed suicide at age 29. The final episodes of Season 4 were devoid of Young, but his character, Det. Barry Frost, hadn't been written out yet. Instead, he was said to be on vacation visiting his mom.

"It was very daunting knowing what was before me and what I had to do," Nash tellsTVGuide.com. "From the moment that I was approached about this show and started watching the episodes ... and [after] I met with Angie [Harmon] and Sasha [Alexander], I knew that doing it in a compelling and respectful way was the most important thing to them for the season."

The farewell will play out over the first two episodes of Season 5, which premieres Tuesdayat 9/8c on TNT. Jane (Harmon) and Maura (Alexander) will learn of Frost's death in a car accident at the end of the premiere, and then the second episode will focus on the grieving squad, culminating with a memorial service, during which Jane speaks. "Angie is fantastic in the scene," Nash teases. "Just incredibly moving and amazing."

Killing off Frost was the only option to honor Young, Nash feels, as any other alternative would ring false. But she was well aware that she had to approach it with great care.

"We had to deal with it in a real and concrete way. We couldn't just say Barry Frost went on vacation and occasionally talk about how much fun he was having or give him a new job in a new city," she says. "That would feel icky. We realized that we had to have the character die so we could deal with that loss the same way the people on the show had dealt with Lee's loss. What comes with that is we had to make sure we were not being exploitive and we were honoring his memory appropriately ... and I think we all feel as a collective that we, to the best of our abilities, accomplished that."

While the second episode will serve as the tribute, Frost's death will continue to resonate, as, in an obviously unplanned twist, it lends a poignancy to the new season as it wrestles with not only loss, but new life. The Season 4 finale, lest we forget, had Jane discovering she was pregnant after breaking up with Casey.

"I'm a big believer that you can't just say something to the audience and say, 'Kidding!'" Nash says. "Jane Rizzoli, for my money, was pregnant at the end of Season 4, and so we are moving forward with her being pregnant. We're going to play with the idea of her being pregnant and what it means for her life, her relationship with Maura, how does she look at raising this child, especially having just lost a friend and a colleague, but not in a somber way. Of them both, I don't think anyone would have thought Jane would be a mother first. It's a very fruitful story line. No pun intended."

The other finale bombshell, of course, found Maura and Jane's little brother Frankie (Jordan Bridges) sharing a kiss. The two awkwardly broach the subject in the premiere, but Maura will soon have a new guy in her life in Jack Keystone (Enver Gjokaj), a Boston University professor, in what Nash describes as a "very interesting" arc.

"There are a lot of fun things this season between that and the pregnancy," Nash says. "We had to deal with this very tough circumstance, a very tough challenge, but at its core, the show is still a fun crime drama about these two friends, and that's one thing that won't change even with all these changes."